This invention relates generally to a reproduction apparatus and method, and more particularly to a reproduction apparatus and method wherein a reading out position of a reading out element for reading out data from a predetermined sector of a predetermined track of a recording medium is moved to read out data from the recording medium.
At present, optical discs, such as compact discs, on which digital data are recorded are widely used. On such optical discs, data are recorded on each of a plurality of sectors of a plurality of tracks formed in circumferential directions on the discs. Each of the plurality of sectors is also provided with a sector address.
When reproducing data recorded on an optical disc making use of an optical pickup, laser light is irradiated upon pits formed on tracks of the optical disc which are positioned to correspond to the stored data being transmitted. Light which is reflected from the pits on the disc is photo-electrically converted, so as to read out the stored data from each sector.
The optical pickup is adapted to move in a radial direction of the optical disc, and thus in a direction perpendicular to a tangent of each circular track of the optical disc, for example, by a drive motor. Accordingly, when data are to be read out continuously from sectors positioned on different tracks, a control circuit for controlling the drive motor calculates the number of tracks the optical pickup must be moved to arrive at the track having the sector to be read out next. This calculation is made from a sector address which represents the current position of the optical pickup and another sector address of a sector to be read out next. The optical pickup is then moved by the required number of tracks.
Next, an example of the calculation of the distance over which the optical pickup is to be moved is described with reference to the flow chart depicted in FIG. 6.
First in step S1, a track number T.sub.t of a target track, which contains a target sector S.sub.t is calculated from the address of the target sector. In a preferred embodiment, the number T.sub.t of the target track is calculated in the following manner. First, the distance along the radius of the disc to the target T.sub.t track which has the target sector address is represented by r. The distance along the radius of the disc from the current track to a reference track which has a reference sector Sr (start point of a program area) is represented by r.sub.0. The track pitch is represented by T.sub.p, the rotational speed (linear velocity) of the optical disc is represented by V1, and the sector frequency is represented by fs. The sector number S.sub.n (number of sectors) of a track located at a radius r is represented by an expression (1). EQU S.sub.n =2.pi.r.times.fs/V1 (1)
In a preferred embodiment, by way of example, in which the optical disc is a DVD (Digital Versatile Disc), r.sub.0 is fixed at 24.00 mm and T.sub.p is fixed at 0.74 .mu.m while V1 is fixed at 3.49 m/s for a single layer disc but fixed at 3.84 m/s for a dual layer disc.
Furthermore, where the number of tracks from the track having the reference sector address S.sub.r to the track which has the target sector address S.sub.t is represented by k, the radius r from the current track to the track having the target sector address S.sub.t is represented by an expression (2). EQU r=r.sub.0 +k.times.T.sub.p (2)
Accordingly, the total number S of sectors which are contained between the track having the reference sector address S.sub.r and the Nth track is represented by an expression (3). ##EQU1##
The expression (3) is a quadratic equation regarding N and may be re-written into an expression (4). EQU .pi..times.fs.times.T.sub.p.times.N.sup.2 +.pi..times.fs.times.(2r.sub.o -T.sub.p).times.N-V1.times.S=0 (4)
Then, solving this equation (expression (4)) for N (track number), N is represented by an expression (5). ##EQU2##
Here, since the radius r.sub.0 to the track having the reference sector is much larger than the track pitch T.sub.p (r.sub.0&gt;&gt;T.sub.p), N may be represented approximately by an expression (6). ##EQU3##
Accordingly, since the track number T.sub.t of the target track is equal to the number of tracks the target track is positioned from the reference track, the track number T.sub.t may be calculated from the sector address St in accordance with an expression (7). ##EQU4##
Thus, the track number T.sub.t of the track containing the next sector to be read may be calculated in this manner. It is to be noted that, from the number T.sub.t of the track, the sector number S.sub.n on the track is calculated in accordance with an expression (8). ##EQU5##
Then, in step S2, from the current sector address S.sub.c of the current sector, the number T.sub.c of the current track on which the current sector S.sub.c is located is calculated in accordance with an expression (9). ##EQU6##
Then, in step S3, it is determined whether or not the number T.sub.t of the target track in which is located the target sector S.sub.t to be read out next is larger than the number T.sub.c of the current track on which the current sector S.sub.c is located. If it is determined that the number T.sub.t of the target track is larger than the number T.sub.c of the current track, then the direction of movement of the optical pickup is set to the forward direction toward the outermost circumference of the optical disc in step S4.
On the other hand, if it is determined in step S3 that the number T.sub.t of the target track on which the target sector S.sub.t is located is equal to or smaller than the number T.sub.c of the current track on which the current sector S.sub.c is located, then the direction of movement of the optical pickup is set to the reverse direction toward the innermost circumference of the optical disc in step S5.
In step S6, an absolute value .vertline.T.sub.t -T.sub.c.vertline. of the difference between the number T.sub.t of the target track on which the target sector S.sub.t to be read next is located and the number T.sub.c of the current track on which the current sector S.sub.c is located determines the number of tracks the optical pickup is to move.
In step S7, it is determined whether or not the movement track number is 0. If it is determined that the movement track number is 0, then movement of the reading out position is stopped. If the movement track number is not 0, then in step S8 the optical pickup is moved the appropriate number of tracks, as determined in step S6. Thereafter, the control returns to step S1 so that it can be confirmed that the target track has been reached. If it is determined that the current track T.sub.c is equal to the target track T.sub.t, then no further movement is performed. However, if T.sub.c is not equal to T.sub.t, movement of the optical pickup is performed repetitively (track jumping) until T.sub.c equals T.sub.t.
In this manner, because when the optical pickup is moved an error may occur, track jumping is performed repetitively until the optical pickup reaches the target track T.sub.t.
However, the method described above is deficient. Since the number T.sub.c of the current track at the current position of the optical pickup and the number T.sub.t of the target track of the destination of the optical pickup, and therefore the required movement of the optical pickup, are calculated for each required track jump and movement of the optical pickup in accordance with expression (7) or expression (9), each of which is a complicated expression including a square root, the calculation of the movement track number takes a long time. Thus, it is difficult to move the optical pickup to the proper position of the target track at a high speed.